It is known to print continuous packaging material and other continuous print media such as label bearing substrates with alphanumeric information and other symbols using a thermal transfer printer. A print head having a row of electronically driven heating elements is brought to bear against an ink-carrying thermal transfer ribbon lying over the print medium while the print medium is driven perpendicularly to the row of print elements. In one known printer, the ribbon is supplied from a take-off spool and then passes along a ribbon path which extends between the print head and the path of the print medium, and thereafter is fed onto a take-up spool, the ribbon travelling across the print head at at least approximately the same speed as the print medium whilst printing is taking place. The path followed by the print medium extends around movable rollers which deflect the print medium by variable amounts both upstream and downstream of the print head. These rollers impose significant stresses on the print medium and complicate threading when the print medium is loaded into the printer. Such a printer operates typically at print medium speeds up to 200 mm per second.